Integrated circuit design flow with layout-dependent effects

ABSTRACT

A design system for designing an integrated circuit that includes a processor, a memory coupled to the processor, and instructions to generate and edit a schematic of the integrated circuit, generate at least one recommended layout parameter of an integrated circuit device within the integrated circuit, extract the at least one recommended layout parameter during a layout stage of the integrated circuit, and calculate a circuit performance parameter of the integrated circuit using the at least one recommended layout parameter, and a user interface configured to display at least one of the circuit performance parameter and layout constraints of the integrated circuit device of the integrated circuit.

BACKGROUND

In an integrated circuit design process, a circuit schematic of an integrated circuit being designed is generated first, for example, in a schematic editor. A pre-layout simulation is performed on the circuit schematic to simulate a performance of the integrated circuit. Since the layout of the integrated circuit has not yet been created at the time the pre-layout simulation is performed, layout-dependent effects (LDEs) of the layout of the integrated circuit cannot be taken into account in the pre-layout simulation. Instead, in the pre-layout simulation, default values of the LDEs are assumed.

Following the pre-layout simulation, the layout of the integrated circuit is generated, for example, using a layout editor. A design verification is then performed on the layout, wherein the design verification includes an LDE parameter extraction, for example.

A post-layout simulation is then performed on the layout. In the post-layout simulation, the LDEs are taken into account, so that the generated circuit performance parameters reflect the actual circuit more accurately. The circuit performance parameters are then compared to the design specification. If the circuit performance parameters meet the requirement of the design specification, the design can be approved. Otherwise, the design process loops back to the schematic generation and editing steps, and the steps including the pre-layout simulation, the layout creation, the design verification, and the post-layout simulation are repeated to modify the design. The loop is repeated until the circuit performance parameters meet the requirement of the design specification.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of a layout-dependent effect (LDE) aware layout design system in accordance with one or more embodiments;

FIG. 2A is a schematic of an integrated circuit to be designed using the system of FIG. 1 in accordance with one or more embodiments;

FIG. 2B is a schematic of a layout of the circuit of FIG. 2A in accordance with one or more embodiments;

FIG. 3 is a flow chart of an LDE-aware circuit layout design method in accordance with one or more embodiments;

FIG. 4 is a block diagram of the LDE Budgeting module of the system of FIG. 1 in accordance with one or more embodiments;

FIG. 5 is a flow chart of the LDE Budgeting operation of the method of FIG. 3 in accordance with one or more embodiments;

FIG. 6 is a flow chart of the LDE constraints checking operation of the method of FIG. 3 in accordance with one or more embodiments; and

FIG. 7 is a block diagram of a general purpose computing device for implementing the design system shown in FIG. 1 in accordance with one or more embodiments.

DETAILED DESCRIPTION

The making and using of the embodiments of the disclosure are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are illustrative, and not intended to limit the scope of the disclosure.

The layout system in accordance with an embodiment enables a look ahead layout-dependent effects (LDE) analysis to reduce the number of iterations performed during the layout design process by prediction and predetermination of LDE parameters during the design of the layout according to design specifications and enables verification of accuracy of the electrical design of the layout.

FIG. 1 illustrates a block diagram of an LDE-aware layout design system 10 for designing the layout of integrated circuits in accordance with one or more embodiments.

Layout design system 10 includes LDE-aware layout module 20, schematic editor 30, layout editor 40, a user interface 50, an LDE budgeting module 60, and an LDE constraints data store 70. In one or more embodiments, LDE-aware layout module 20, schematic editor 30, layout editor 40 and LDE-budgeting module 60 are sets of executable instructions.

Schematic editor 30 is configured to be used to generate and edit circuit schematics of integrated circuits that are being designed. Schematic editor 30 is also configured to generate a pre-simulation of the circuit schematics. According to one or more embodiments, schematic editor 30 includes a set of executable instructions for generating the pre-simulation of the schematic. In other embodiments, a separate device (e.g., a simulator) in communication with the schematic editor 30 is used to generate the pre-simulation of the schematic. Layout editor 40 is configured to be used to generate and edit layouts of the integrated circuits in accordance with the circuit schematics generated by the schematic editor 30. LDE-aware layout module 20 is configured to extract layout parameters (LDE parameters) from the layout generated by layout editor 40 and calculate circuit performance parameters related to circuit performance of the circuit via computing device 700 (depicted in FIG. 7).

User interface 50 is configured to receive and display the circuit schematic from schematic editor 30, the layout from layout editor 40, and the LDE parameters extracted from the layout and calculated circuit performance parameters via LDE-aware layout module 20. User interface 50 is also configured to receive user inputs to adjust the circuit schematics and the layout and to select specific devices in order to display circuit performance parameters of specific devices selected by a user.

LDE budgeting module 60 is configured to generate layout constraints according to electrical specifications and potential degradation and area tolerance of the selected devices. The generated layout constraints are stored in and retrieved from the constraints data store 70. Upon request, the constraints are sent to the LDE-aware layout module 20 via the schematic editor 30 and are used to modify the LDE parameters (e.g., to optimize the LDE parameters). The communication between components 20 through 70 are schematically illustrated by arrows in FIG. 1.

An integrated circuit includes a plurality of devices, and the layout design system 10 enables design and layout optimization at a device level (i.e., one or more devices) within the integrated circuit according to one or more embodiments.

FIG. 2A is a schematic view of an exemplary integrated circuit 150 to be designed by the method 300 shown in FIG. 3 in accordance with one or more embodiments. The circuit 150 is an inverter including a PMOS transistor 155 and an NMOS transistor 156 having both drains and gates thereof interconnected. Other circuits to be designed are within the scope of various embodiments.

FIG. 2B is a schematic of a layout of the circuit of FIG. 2A, in accordance with one or more embodiments. In the layout, PMOS transistor 155 includes an active region 160 and a gate 161 formed over the active region 160. NMOS transistor 156 is formed within a p-well region 162 and includes an active region 163 and the gate 161 formed over the active region 163. Dummy gate electrodes 164 and 166 are formed adjacent to the transistors 155 and 156.

FIG. 3 is a flow chart of an LDE-aware circuit layout design method 300 within one or more embodiments.

In operation 310, a pre-layout simulation of the circuit 150 to be designed is generated. The pre-layout simulation is performed via schematic editor 30. From operation 310, the process continues to operation 320 where a layout (e.g., as shown in FIG. 2B) of the circuit design is created via the layout editor 40 based on the pre-layout simulation generated in operation 310. Individual devices (e.g., transistors 155 and 156) of the circuit 150 are placed in desired locations via the layout editor 40, and design layout constraints are checked by the layout editor 40, to prevent violation of design rules.

From operation 320, the process continues to operation 330, where a simulation is generated via the schematic editor 30 or separate device (e.g., a simulator) with LDE parameters being taken into consideration. The LDE parameters include, and are not limited to, the parameters related to well proximity effect (WPD), OD-spacing effect (OSE), poly-spacing effect (PSE), length of diffusion (LOD) effect, and boundary effect, etc. From operation 330, the process continues to operation 340 where, the method includes modifying the circuit based on the simulation created in operation 330, to thereby compensate for LDE impact. For example, if the circuit performance does not meet the circuit specification due to the LDE impact, the geometry of the devices within the circuit is enlarged to compensate for potential degradation. In one or more embodiments, if necessary, the circuit topology is modified and the process is repeated beginning at operation 310.

Next, in operation 350, LDE budgeting is performed via the LDE budgeting module 60 to enter constraints, tolerated device degradation (e.g., for transistors 155 and 156), area constraints for the devices of the circuit 150 and other parameters associated with the circuit 150 being designed. The LDE parameters are modified based on the design constraints for optimum performance of the circuit 150. Details regarding the LDE budgeting operation will be discussed below with reference to FIGS. 4 and 5.

From operation 350, the process continues to operation 360 where layout placement is fine-tuned and the layout is finalized. In operation 360, routing is performed to layout metal lines used for interconnecting the devices (e.g., transistors 155 and 156) in the circuit 150. The layout is finalized (i.e., completed) by creating an LDE-aware layout (operation 370) and by checking LDE constraints (operation 380). According to one or more embodiments, operations 370 and 380 are performed independently from each other.

In operation 370, the LDE-aware layout is created by first extracting LDE parameters determined via the LDE budgeting module 60, and then determining circuit performance parameters via LDE-aware layout module 20 (as depicted in FIG. 1) using the extracted LDE parameters. LDE-aware layout module 20 determines circuit performance parameters, e.g., drive currents, threshold voltage, transconductance, and the like, corresponding to the devices (e.g., transistors 155 and 156) within the layout. According to an embodiment, the extraction of LDE parameters and determination of circuit performance parameters are performed by the computing device 700, and are performed simultaneously with the layout creation without waiting for the layout of the entire circuit 150 to be completed. The circuit performance parameters are viewable by the user via the user interface 50.

Additional details regarding performance of pre-layout simulation, layout creation and simulation with LDE parameter consideration, and creating an LDE-aware layout in corresponding operations 310, 320, 330 and 370, can be found in co-pending application Ser. No. 13/115, 752 filed on May 25, 2011, entitled “On-the-Fly Device Characterization from Layouts of Circuits”, the entire contents of which are incorporated by reference herein.

After creating the LDE-aware layout in operation 370, the process returns to operation 360.

From operation 360, the process then continues to operation 380 where an LDE-constraints checking process is performed to confirm that design constraints have not been violated when the LDE impacts are considered. Additional details regarding operation 380 will be discussed with reference to FIG. 6.

After the completion of operation 380, the process returns to operation 360 and the layout is finalized. From operation 360, the process then continues to operation 390.

In operation 390, a post-layout simulation is generated via schematic editor 30 and then a layout is generated via layout editor 40 based on final evaluation results.

At operation 400, an interactive LDE impact analysis is performed where an analysis of the circuit performance parameters for the devices are analyzed by the user via the user interface 50, using a predetermined algorithm and/or set of instructions stored within the LDE budgeting module 60. According to one or more embodiments, operation 400 is performed as a part of the post-layout simulation performed in operation 390. Further, according to other embodiments, operation 400 is performed as a separate analysis tool. The analysis includes changes in the circuit performance parameters based on the set design constraints as set by the user and LDE-parameter recommendations determined by the LDE budgeting module 60. The analysis is performed on the final layout and includes comparison data between the set design constraints and recommendations. In addition, the analysis includes an overall analysis of the cost and degradation reduction of the devices, for example. The analysis further includes statistical data of the LDE degradation of each device in various different formats (e.g., in a histogram).

After the post-layout simulation is performed at operation 390, the circuit performance parameters of the entire circuit 150 are generated using the LDE-aware layout module 20, and are compared to the requirements of the design specification using the LDE budgeting module 60. From operation 390, the process continues to operation 405 where it is determined whether the circuit parameters meet the requirements of the design specifications. In one or more embodiments, the method loops back to step 310 to modify the layout design if the circuit performance parameters do not meet the requirements of the design specifications. Otherwise, if circuit performance parameters meet the requirements of the design specifications, the circuit 150 and the layout thereof are approved at operation 410 via the user using the layout editor 40, and the user determines the design is complete. At this stage of the method, the user can begin preparation work for chip implementation e.g., design kits implementation, based on the completion of the layout design and the chip is then implemented.

FIG. 4 is a detailed block diagram of LDE budgeting module 60 of the system of FIG. 1.

As shown in FIG. 4, the LDE budgeting module 60 is in data communication with the schematic editor 30. The LDE budgeting module 60 comprises a budgeting manager 62, an optimizer 64 and an expression evaluator/simulator 65. According to one or more embodiments, LDE budgeting module 60 is separate from the schematic editor 30. According to other embodiments, LDE budgeting module 60 is integrated (i.e., included) within schematic editor 30. Details regarding the operation of the LDE budgeting module 60 will be discussed below with reference to FIG. 5. Effectively, FIG. 5 is a flow chart of LDE budgeting operation 350 of the method of FIG. 3 in accordance with one or more embodiments.

LDE budgeting module 60 receives circuit performance parameters corresponding to selected devices (e.g., transistors 155 and 156) of the layout from schematic editor 30. The process of performing LDE budgeting (operation 350 shown in FIG. 3), begins at operation 351 as shown in FIG. 5, where the user views circuit 150 being designed at a display of user interface 50 and sets predetermined design constraints (e.g., electrical and area constraints) of circuit 150 through schematic editor 30. The design constraints are stored within constraints data store 70. From operation 351, the process continues to operation 352, where LDE budgeting module 60 receives the design constraints stored in data store 70 or in real-time while being set by the user. Upon receiving the design constraints, information including a cost function of the circuit 150 being designed and layout variables, for example, of the circuit performance parameters are selected from the received information via the budgeting manager 62 of the LDE budgeting module 60. According to one or more embodiments, the information also includes specific tolerance ranges including electrical tolerances. The information is processed via optimizer 64 shown in FIG. 4. Optimizer 64 modifies the LDE parameters of one or more devices (e.g., transistors 155 and 156) within the circuit 150 for optimum performance according to the design constraints, by selecting sample points from the information, and transmitting the sample points to the expression evaluator/simulator 65 for evaluation. Evaluation results determined in operation 352 are sent to the budgeting manager 62 either directly from the expression/evaluator simulator 65 or indirectly from the optimizer 64. Based upon evaluation results, the LDE budgeting module 60 determines LDE-parameter recommendations for the required LDE parameters at operation 353, and transmits the recommendations to the schematic editor 30, to predict post-layout effects of the LDE parameters (as performed in operation 360 shown in FIG. 5). A back-annotating process is performed by which the LDE parameters are back-annotated to schematic where the default LDE parameters are replaced with the extracted LDE parameters. Because the operations 351, 352, and 353 are performed and the recommended LDE parameters are back-annotated to schematic, the LDE parameters are included in the pre-simulation.

At operation 354, the results of the pre-simulation and post-simulation operations (operation 310 and operation 390 shown in FIG. 3) are then correlated since the layout is driven by the same LDE parameters. For example, by setting the electrical tolerance as an optimal constraint and performing operation 354, the pre-layout simulation with back-annotated LDE parameters more closely corresponds to the post-layout simulation.

FIG. 6 is a flow chart of the LDE constraints checking operation 380 of the method 300 of FIG. 3 within one or more embodiments. As shown, in operation 382, design constraints are set including LDE constraints based on both absolute and mismatch criteria. The design constraints include mathematical expressions of the LDE-aware layout, relations between different devices and cost functions including area cost. Information including the cost functions, and electrical constraints (i.e., set by the user goal and based on cost functions) is retrieved from the LDE budgeting module 60. The mathematical expressions include setting absolute values for electrical parameters and circuit functions, and tolerances for electrical degradation including mismatch tolerances for matched instances, and determining a weighted priority of the design constraints.

From operation 382, the process continues to operation 383, where a layout placement is repeated based on the design constraints set in operation 382. In one or more embodiments, the layout placement performed in operation 383 is the same as that performed in operation 360. In other embodiments, LDE budgeting operation 350 is skipped, and performed independent of the layout placement operation, along with LDE-aware layout operation 370, LDE constraints checking operation 380 and LDE impact analysis operation 400 (discussed above) such that if the layout placement in operation 383 is performed by another method, these operations can be implemented to perform LDE constraint checking on the layout.

A check is then performed in operation 384, to calculate electrical characteristics of one or more of the devices of the circuit 150 and degradation thereof based on LDE impact. Further, an evaluation of the design constraints is performed using the calculations by comparing the calculations with the design constraints. Operation 384 is performed before performing routing (i.e., adding wiring interconnects to the circuit design). In one or more embodiments, operation 384 is performed after routing.

From operation 384, the process continues to operation 385 where the results of the check performed including any violations, are sent to the layout editor 40 accessible by the user via the user interface 50 in an interactive query and/or stored within an associated database for later use.

FIG. 7 is a block diagram of a general purpose computing device 700 for implementing the design system shown in FIG. 1 in accordance with one or more embodiments.

Computing device 700 is a data or information processing device such as a CAD tool, a personal computer or a workstation. As shown, the device 700 includes a memory unit 701 for storing circuit information and other information such as design rules, control unit 702 for carrying out operations for the design of a layout as shown in FIGS. 3 through 6, and an output unit 703 for supplying the design results. The computing device 700 further includes the user interface by which a user enters instructions as input. The control unit 702 includes a controller or processor 706 (e.g., a CPU) for executing prescribed processes in accordance with programs, and a computer readable storage medium 707 for storing programs in the form of computer program code i.e., a set of executable instructions. The design method for designing an integrated circuit device is a software program comprising one or more sets of executable instructions stored within the computer readable storage medium 707 for execution by processor 706 according to one or more embodiments. In other embodiments, processor 706 is an application specific integrated circuit configured with one or more hardwired sets of instructions for execution. In some embodiments, the computer readable storage medium 707 is an electronic, magnetic, optical, electromagnetic, infrared, and/or a semiconductor system (or apparatus or device). For example, the computer readable storage medium 707 includes a semiconductor or solid-state memory, a magnetic tape, a removable computer diskette, a random access memory (RAM) a read-only memory (ROM), a rigid magnetic disk, and/or an optical disk. In some embodiments, using optical disks, the computer readable medium 707 includes a compact disk-read only memory (CD-ROM), a compact disk read/write (CD-R/W), and/or a digital video disc (DVD).

In one or more embodiments, the computing device 700 is a component within the LDE-aware module 20. In other embodiments, the LDE-aware module 20 and the LDE budgeting module 60 are software modules of a computing device such as computing device 700.

One or more embodiments include a design system for designing an integrated circuit that includes a processor; a memory coupled to the processor; and a computer-usable medium embodying computer program code, the computer program code comprising instructions executable by the processor and configured to perform at least one of the following steps of generate and edit a schematic of the integrated circuit, generate at least one recommended layout parameter of an integrated circuit device within the integrated circuit, extract the at least one recommended layout parameter during a layout stage of the integrated circuit, and calculate a circuit performance parameter of the integrated circuit using the at least one recommended layout parameter; and a user interface configured to display the circuit performance parameter and layout constraints of the integrated circuit device of the integrated circuit.

One or more embodiments include a computer readable medium comprising computer executable instructions for carrying out a method for designing an integrated circuit. The method comprising generating a pre-layout simulation of an integrated circuit; generating a first layout according to a schematic of the integrated circuit based on the pre-layout simulation; generating a simulation of the integrated circuit with predetermined layout parameters; modifying the integrated circuit to compensate for an impact of the layout parameters within the simulation; budgeting the layout parameters based on design constraints of the integrated circuit and generating at least one recommended layout parameter based on the budgeting; generating a second layout based on the at least one recommended layout parameter; comparing the at least one recommended layout parameter to the design constraints for violations; and generating a post-layout simulation using the at least one recommended layout parameter, to simulate performance of the integrated circuit.

One or more embodiments include a computer readable medium comprising computer executable instructions for carrying out a method for designing an integrated circuit. The method comprising generating a first layout according to a schematic of an integrated circuit based on a pre-layout simulation; generating a simulation of the integrated circuit with predetermined layout parameters; modifying the integrated circuit to compensate for an impact of the layout parameters within the pre-layout simulation; budgeting the layout parameters of an integrated circuit device of the integrated circuit based on design constraints of the integrated circuit and generating at least one recommended layout parameter based on the budgeting; generating a second layout based on the at least one recommended layout parameter by back-annotating the predetermined layout parameters used in the simulation; comparing the at least one recommended layout parameter to the design constraints for violations; and generating post-layout simulation using the at least one recommended layout parameter, to simulate performance of the integrated circuit.

Although the embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. In addition, each claim constitutes a separate embodiment, and the combination of various claims and embodiments are within the scope of the disclosure. 

What is claimed is:
 1. A non-transitory computer readable medium comprising computer executable instructions for carrying out a method for designing an integrated circuit, the method comprising: performing a pre-layout simulation of a circuit design of the integrated circuit; generating a first layout according to a schematic of the circuit design based on the pre-layout simulation; performing a simulation of the circuit design with predetermined layout parameters; generating a modified circuit design of the integrated circuit by modifying a circuit of the circuit design to compensate for an impact of the layout parameters according to the simulation; budgeting the layout parameters for the modified circuit design based on design constraints of the integrated circuit and generating at least one recommended layout parameter based on the budgeting; generating a second layout based on the modified circuit design and the at least one recommended layout parameter; comparing the at least one recommended layout parameter to the design constraints for violations; and performing a post-layout simulation of the modified circuit design based on the second layout.
 2. The computer readable medium of claim 1, wherein budgeting comprises: receiving a circuit performance parameter for an integrated circuit device; receiving in real-time, predetermined design constraints as set by a user; and determining the at least one recommended layout parameter for the integrated circuit device based on the predetermined design constraints.
 3. The computer readable medium of claim 2, wherein budgeting further comprises: determining information including at least one of cost function of the circuit, layout variables, and tolerance ranges of the integrated circuit device; modifying the predetermined layout parameters based on the information determined; and evaluating sample points of the information and generating evaluation results.
 4. The computer readable medium of claim 3, wherein budgeting further comprises back-annotating the predetermined layout parameters based on the evaluation results generated.
 5. The computer readable medium of claim 3, wherein budgeting further comprises: correlating electrical tolerance data of the integrated circuit device for generating pre-layout simulation and post-layout simulation.
 6. The computer readable medium of claim 5, wherein generating the second layout comprises: extracting the layout parameters of the integrated circuit device; calculating the circuit performance parameter of the integrated circuit device; and displaying the circuit performance parameter of the integrated circuit device on a user interface.
 7. The computer readable medium of claim 2, further comprising: performing a check of the at least one recommended layout parameter to determine whether predetermined design constraints are violated.
 8. The computer readable medium of claim 7, wherein performing the check comprises: setting design constraints including mathematical expressions of the second layout, and relations between integrated circuit devices of the integrated circuit within the second layout; generating a check layout based on the design constraints; calculating degradation characteristics of the integrated circuit device in the check layout generated and evaluating the design constraints based on the calculations by comparing the calculations with the design constraints; and reporting any violations to the design constraints by the at least one recommended layout parameter.
 9. The computer readable medium of claim 1, wherein generating a second layout further comprises: routing metal lines to interconnect devices in the second layout.
 10. A non-transitory computer readable medium comprising computer executable instructions for carrying out a method for designing an integrated circuit, the method comprising: generating a first layout according to a schematic of a circuit design of the integrated circuit based on a pre-layout simulation; performing a simulation of the circuit design with predetermined layout parameters; generating a modified circuit design of the integrated circuit by modifying a circuit of the circuit design to compensate for an impact of the layout parameters according to the simulation; budgeting the layout parameters of an integrated circuit device of the modified circuit design based on design constraints of the integrated circuit and generating at least one recommended layout parameter based on the budgeting; generating a second layout based on the modified circuit design and the at least one recommended layout parameter by back-annotating the predetermined layout parameters used in the simulation; comparing the at least one recommended layout parameter to the design constraints for violations; and performing a post-layout simulation of the modified circuit design based on the second layout.
 11. A method of designing an integrated circuit, comprising: generating a first layout according to a schematic of a circuit design of the integrated circuit; performing a simulation of the circuit design with predetermined layout parameters; generating a modified circuit design of the integrated circuit by modifying a circuit of the circuit design to compensate for an impact of the layout parameters according to the simulation; budgeting the layout parameters of an integrated circuit device of the modified circuit design based on design constraints of the integrated circuit and generating at least one recommended layout parameter based on the budgeting; and generating, using a computer, a second layout based on the modified circuit design and the at least one recommended layout parameter.
 12. The method of claim 11, further comprising: comparing the at least one recommended layout parameter to the design constraints for violations; and performing a post-layout simulation of the modified circuit based on the second layout.
 13. The method of claim 11, wherein the budgeting comprises: receiving a circuit performance parameter for an integrated circuit device; receiving in real-time, predetermined design constraints as set by a user; and determining the at least one recommended layout parameter for the integrated circuit device based on the predetermined design constraints.
 14. The method of claim 13, wherein the budgeting further comprises: determining information including at least one of cost function of the circuit, layout variables, and tolerance ranges of the integrated circuit device; modifying the predetermined layout parameters based on the information determined; and evaluating sample points of the information and generating evaluation results.
 15. The method of claim 14, wherein the budgeting further comprises: back-annotating the predetermined layout parameters based on the evaluation results generated.
 16. The method of claim 13, wherein the budgeting further comprises: correlating electrical tolerance data of the integrated circuit device for generating pre-layout simulation and post-layout simulation.
 17. The method of claim 16, wherein the generating the second layout comprises: extracting the layout parameters of the integrated circuit device; calculating the circuit performance parameter of the integrated circuit device; and displaying the circuit performance parameter of the integrated circuit device on a user interface.
 18. The method of claim 13, further comprising: performing a check of the at least one recommended layout parameter to determine whether predetermined design constraints are violated.
 19. The method of claim 18, wherein the performing the check comprises: setting design constraints including mathematical expressions of the second layout, and relations between integrated circuit devices of the integrated circuit within the second layout; generating a check layout based on the design constraints; calculating degradation characteristics of the integrated circuit device in the check layout generated and evaluating the design constraints based on the calculations by comparing the calculations with the design constraints; and reporting any violations to the design constraints by the at least one recommended layout parameter.
 20. The method of claim 11, wherein the generating the second layout comprises: routing metal lines to interconnect devices in the second layout. 